Lecture 3: Workplace Design Physical work

Transcription

1 Lecture 3: Workplace Design Physical work ENVD 5380 Human Factors/Ergonomics in Environmental Design By Su-Jeong Hwang Shin, Ph.D.

2 Physical work Occupational injuries About 25 % of all occupational injuries (Bureau of Labor Statistics) Occupations, including professional-technical workers, nurses, service workers, all. Human work Stress refers to some undesirable condition or task. Heavy work, noise, sleep loss, boredom, etc. Strain refers to the effects of the stress on the individual. It can be measured in blood chemistry, oxygen consumption, electrical activity of the muscles or the brain, heart rate, body temperature, work rate, errors and attitudes. Reference from Text book Sanders (Ch. 8, 9, 10, 13)

3 Work Spaces Work space envelopes: It means the 3 dimensional space within which an individual works. (e.g. the space within which the hands are used.) This topic is related to physical space and arrangement. Related to the concept of work space envelopes: Out-of- reach requirements The distances required to prevent a person from reaching something (Usually hazardous) over a barrier. Clearance requirements The minimum space needed to move through a tight space or perform work in a confined area.

4 Work-space envelopes for seated personnel The limits of the work-space envelope for seated personnel Determined by functional arm reach Nature of the manual activity (e.g. the task or function) to be performed. Functional arm reach are influenced by the factors: Effects of direction of reach and presence of restraints on work-space envelope. Effects of manual activity on work-space envelope. Effects of apparel on work-space envelope.

5 Effects of direction of reach Effects of direction of reach and presence of restraints on workspace envelope. Results based on the study (Roth, Ayoub,& Halcomb) They measured the functional arm reach of subjects at various lateral angles from a dead-ahead seated position (from -45 left to +120 right) and at various levels (ranging form -60 to 90 ) from a seat reference point (SRP). Measurements were taken of the grip-center reach point at 114 such locations, under both restrained and unrestrained conditions. In the restrained conditions The shoulders were held back against the seat back In the unrestrained conditions The subjects could move their shoulders. The type of restraint can influence the functional arm reach. Based on study of comparing three types of vehicle seat restraint (Garg, Bakken, and Saxena). The less the restriction, the further the reach.

6 Effects of direction of reach

7 Effects of manual activity Effects of manual activity on work-space envelope. Grip strength and the dynamic reach envelope (= kinetosphere) Hand grasp: thumb tip measurement are about 2 in or more shorter than finger tip measurements (Bullock,1974). Different hand grasp actions influence the space envelope. Dempster s study involved grasping a handlelike device with the hand in 1 of 8 fixed orientations (Supine, prone, inverted, and at five spatial angles). Photographic traces of contours of the hand and the movement. Kinetoshere is developed for each grasp, showing mean of three angles: top (transverse), front (coronal), and side (sagittal). The shaded areas indicates the various types of hand grips could most adequately be executed by people.

8 Strophosphere of Kinetoshperes Hand movements

9 Effects of apparel Effects of apparel on work-space envelope. The apparel worn by people can restrict their movements and the distances they can reach, and can influence the size of the work space envelope. Winter jackets restricted reach by 2 inches.

10 Work-space envelopes for standing personnel Standing reach is a matter of body equilibrium The reach envelop will be modified by any factor. Reach is diminished if a weight is carried in the reaching hand or if an obstacle is placed behind a person that limits counterbalancing activities. The Zone of Convenient Reach (ZCR) ZCR as the space in which an object may be reached within arm s reach. (Pheasant s study).

11 Standing ZCR

12 Work-space envelops Discussion of Work-space envelopes The reasonable limits of such space are determined by functional arm reach Functional arm reach is influenced by such variables as: Direction of arm reach The nature of the manual activity The use of restraints Apparel worn The angle of the backrest Personal variables such as age, sex, ethnic group, and handicaps. Design such space for the 5 th percentile of the using population, thus making it suitable for 95 percent of population. Consider special populations the design of the work space requires particular attention.

13 Design: Out of reach Out of reach requirements Things not to be touched (e.g. children play room) Design space, a barrier of some height is place between the person and the object. How far? It depends on: 1) the height of the barrier 2) the height of the object. Example: Thompson s study using males of the 99th percentile in stature measured maximum reach for various combinations of these two variables (see Sanders, Figure 13-9, p. 430).

14 Design: Out of reach

15 Design: Clearance Clearance requirements Move through, work in, or just fit into spaces. Example: some unusual circumstances, such as the sleeping space needed by long haul truck drivers. Sanders study reports the dimensions of the preferred and prostrate (face-down) postures of the 95th percentile drivers.

16 Design: Clearance

17 Design of work surfaces Work surfaces Within the envelope of a workplace, specific design decisions need to be made about various features of the workplace, the location and design of work surfaces e.g. surface involved benches, desks, tables, etc. Examples of the work surfaces: Horizontal work surface area Work surface height: seated Work surface height: standing

18 Design: Horizontal work surfaces Horizontal work surface area To be used by seated and sit stand should provide for manual activities to be within convenient arm s reach. Work surface area definition and dimensions Normal area and maximum area Normal area: The area can be conveniently reached with a sweep of the forearm while the upper arm hangs in a natural position at the side. Maximum area: The area could be reached by extending the arm from the shoulder. Work surface area with the dynamic interaction of the movement of the forearm as the elbow is moving.

19 Working Area (NWA or MWA) Normal working are (NWA) NWA allows hand motion to be made in a convenient zone with normal energy expenditure. Area described by the arms and hands with the elbows flexed at ~90 degree. Typically, the comfortable limit of outward rotation is about 25 degree. Maximum working area (MWA) MWA is the intersection of the ZCR with the horizontal surface such as table or bench.

20 Horizontal Work Surfaces Slanted surfaces for visual tasks: Subjects using slanted surfaces (12 and 24 ) had better posture, Less trunk movement, less fatigue, and less discomfort than when using horizontal surfaces. Slanted surfaces 15 Less bending of the neck, more upright trunk

21 Design: Work surface height Work surface height: seated Work surface height: The height of the upper surface of a table, bench, desk, counter, measured from the floor. Working height: Depends on what one is working on. When wiring on paper: the working height =the work surface height. When using a keyboard: above the work surface height When washing vegetables in a sink: below the work surface height. Seated work-surface height and arm posture Reducing work surface heights to permit relaxed postures of the upper arms with respect to working height. The heights of desks have been reduced from about 28.5 in Europe but, further reduction of the heights to about 27.

22 Seated work surface height and nature of the task

23 Design: Work surface height Work surface height: seated Seated work-surface height and thigh clearance Influenced by seat height, the thickness of the work surface, and the thickness of the thighs. The clearance between the seat and the underside of the work surface should accommodate the thighs of the largest user as the minimum height for the underside of a nonadjustable seated work surface (ANSI). Problems for smaller people (e.g. raising chair, foot rest.) A range of height adjustments 20.2 to 26.2 (ANSI). General principles for seated work surfaces The work-surface height should be adjustable to fit individual physical dimensions and preferences. The work surface should be at a level that places the working height at elbow height. The work surface should provide adequate clearance for a person s thighs under the work surface.

24 Design: Work surface height Work surface height: Standing The surface height is related to the nature of task. Heights for precision work, light work, and heavy work as related to elbow height For light and heavy work are below elbow height For precision work is slightly above elbow height.

25 Design: Work surface height The surface height is related to the individual preferences

26 Design Ergonomic Chair Why an ergonomic chair? The average office loses over $7300 per employee per year in poor productivity and medical and workers compensation claims (the bureau of labor statistics). Over 50% are low back injuries. Poor chair design contributes to poor seated posture which plays a major role in these injuries (e.g. secretary back syndrome). Musculoskeletal discomfort (Ong et al., in work with computers, ,1989) Survey of 672 full-time computer users complaints related to poor ergonomic furniture, including the chair. Musculoskeletal discomfort (Ignatius et al., Journal of Human Ergology, 22, 83-93, 1993) Survey of 170 women typists working at computers, Mismatch between chair height and desk height and poor furniture design related to symptoms.

27 Myths of ergonomic seating Ergonomic seating always requires a single, cubist (90 degree upright) postural orientation that is independent of the user s task. You can judge how ergonomic a chair is by briefly sitting in it. Users should be able to adjust everything. Users don t need training on how to sit in a chair. One chair design will provide the best fit for all users.

28 Principles of ergonomic seat design Promote Lumbar Lordosis Definitions: In standing, lodotic inward arch: the lumbar portion of the spine (the small of the back, just above the buttocks) is naturally curved inward (concave) In sitting, Kyphotic ourward bend (convex). Lumbar kyphosis results in increased pressure on the discs. Reclined postures often are preferred. In unsupported sitting or forward leaning the lumbar spine may be in kyphosis, which is undesirable. During supported sitting the lumbar spine should be maintained in lordosis by an adjustable lumbar support. The use of a 2 inch thick lumbar support had a impact on maintaining lumbar lordosis with a seat backrest angle of 90 degree. When the backrest angle was reclined to 110 degree, the lumbar spine resembled closely the lumbar curve of a person standing. A forward-tilting seat produce a more relaxed posture. Lordotic effect of forward-tilting seats was small and depended on other factors such as seat height and table top slant.

29 Promote Lumbar Lordosis

30 Principles of ergonomic seat design Minimize disc pressure Lumbar disc pressure varies with back postrue and the load in the hands. Unsupported sitting in an upright, erect posture (forced lordosis) resulted in a 40 % increase in pressure compared to standing. Unsupported sitting in a forward slumped posture increased pressure 90% compared to standing. Use of a reclined backrest has an effect with reductions in pressure by reclining backrests from vertical (90 ) to 100 to 110 Use of a lumber support reduces disc pressure as does the use of arm rests

31 Principles of ergonomic seat design Minimize static loading of the back muscles Back muscle pain Backrest angle and muscle activity: Muscular activity as measured by electromyography (EMG) is similar when standing or witting. EMG activity decreases when sitting in a forward slumped posture, even though maximum pressure on the discs. A reduction in muscular activity in the back when the backrest was reclines up to 110 degree.

32 Principles of ergonomic seat design Reduce postural fixity The problems of postural fixity, sitting in one position for long periods without postural movement were found. Postural fixity promotes static loading of the back and shoulder muscles, restriction in blood flow to the legs, discomfort. Chair design can reduce postural fixity some by allowing the user to rock in the chair and assume a variety of postures.

33 Principles of ergonomic seat design Adjustment features for an ergonomic chair Seat height Backrest height Ability to turn while seated Back tilt adjustment Adjustable arms Seat tilt adjustment Ability to lean back Ability to track posture changes Carpet casters/ hard floor casters Intuitive, easy to use control

34 Principles of ergonomic seat design Provide for easy adjustability Providing adjustable seats increases productivity. Reduces complaints of shoulder and back pain. People are not aware of the adjustability features and rarely use. About 10% adjusted their seats during the day. Adjustment frequency is higher for older workers than younger people. Guidelines for increasing the use (Lueder s study): Controls can be easily reached and adjusted Instructions on the furniture are easy to understand Controls are easy to find and interpret Tools are not necessary. Controls provide immediate feedback The direction of operation of controls is logical and consistent Few motions are required. Adjustments require the use of only one hand.

35 Ergonomic chair recommendations Seat height and slope Minimum range of 16 to 20.5 in based on a compressed seat (ANSI) 5 to 15 forward tilt to 5 backward tilt. Seat depth and width Chairs depth Should not exceed 16.8 and the width of the seat surface be not less than Seat depth: 15 to 17 in (ANSI) Seat width: 18.2 in (ANSI) Contouring and cushioning Seat cushion thickness range from 11.5 to 2. Seat back parameters Seat back angle: a minimum range of 90 to 105 with the seat pan. up to 120 (ANSI) Seat back width: at least 12 in the lumbar region. Seat back height: a minimum of As a backrest reclines, the lumbar support moves upward relative to the lumbar spine.

36 Ergonomic chair recommendations

37 Dynamic vs. static sitting Dynamic vs. static sitting study (Van Dieen et al, ergonomics, June, 2001) They tested 3 chairs (fixed angle, dynamic angle A, and dynamic angle B) Subjects worked for 3 hours on CAD, word processing and reading tasks. Measured spinal elongation, neck posture, back EMG. Spinal elongation significantly greater for dynamic chairs. Neck posture unaffected by dynamic sitting. Back EMG depends on the task.

38 Effects of a chair headrest Effects of a chair headrest study (Monroe et al., 2001, proc. HFES, 1, ). Studied effects of a reclined posture with headrest on typing. Found significantly less muscle activity with this posture for: Neck (>35% reduction) Back (>34% reduction) Found no differences in typing accuracy.

39 Workstation evaluation

40 Discussion Bias thoughts in environmental design?

41 Discussion The design of work space includes: Work envelop, Work surfaces, Seats, and the Design and Location of equipment. Related to the subject of the design work places, what are the examples of work situations were not well designed? Related to the subject, what are the good examples of ergonomic design applications in environmental design?

42 Sewing-related disorders Sarder, MD, et al (2006). Ergonomic Workplace evaluation of an Asian Garment Factory. Journal of Human Ergology. 35 (1),

43 Assignment # 2 Write a report about Anthropometric theory and Applications (sewing manufacture layout, clothing fit, sizing systems, functional clothing etc.). Format: a single space, 5-6 pages, 12 fonts, Include text citations and references (APA style). Should incorporate at least 1~2 references from professional journals.

44 Assignment # 2 Contents Title and your name Introduction Objectives Method Findings Conclusions/Discussions References Presentation in Power point